Walking beam furnaces are known for providing rectilinear motion of a work product through a furnace chamber in an incremental or step-wise manner. This substantially frictionless transport mechanism minimizes particle generation resulting from abrasion commonly encountered in pushing or sliding type transport devices. The distance a work product is moved through a furnace environment is related to the distance the beam or beams is advanced in each forward increment.
For a variety of reasons, including cost and ease of manufacture, walking beam mechanisms are commonly made from metals able to withstand ordinary furnace temperatures. However, process steps requiring extremely high temperatures exceed the material limits of ordinary metal furnace components which are susceptible to deformation or failure at these elevated temperatures. Additionally, certain thermal treatments require rapid transition of a work product from one thermal zone to another. However, the thermal shock encountered by the walking beam components that move with the work product can cause failure of beam components.
To surmount the limitations of ordinary metal furnace components, ceramic materials are commonly used in high-temperature structures. "High-temperatures" are generally defined as being above 1,830.degree. Fahrenheit (1,000.degree. C.), or temperatures at which, because of melting or oxidation, common metals cannot be used. Ceramics known as refractories are products which are employed in the furnace art to thermally insulate furnaces that produce steel, aluminum and other metals. Refractories are commonly used in the steel industry where they are used for the lining of blast furnaces, open hearth furnaces, nonferrous metallurgical furnaces, ceramic kilns and the like. Common refractory materials include silicon carbide (SiC) and aluminum oxide (alumina). When objects made of refractory materials are configured as simple structures having few angular edges and bends, they can be rapidly transported from one thermal regime to another, e.g., from hot to cold, without suffering from material failure due to thermal shock. In addition to their high temperature tolerances these materials are also extremely hard.
Refractories are known for use with walking beam furnaces, as described in U.S. Pat. No. 4,446,385 to Denis, which discloses refractory walking beams positioned on crosspieces supported by uprights. However, neither the crosspieces nor the uprights of Denis are made of a refractory material because they are not subjected to the high temperatures that the walking beams are exposed to. Instead of providing support and movement elements that are extraordinarily heat tolerant, the Denis furnace isolates these components from extreme temperatures by heat conducting recesses or channels. These recesses direct heated gasses to provide a means for heating the underside of a work piece resting on the hearth without heating the support and movement elements. This configuration is an unnecessarily complex solution for ensuring uniform heating of the work product.